The present invention relates to industrial controllers for the real time control of industrial processes, and in particular to an input/output (I/O) card providing for extremely fast control response to certain signals from the industrial process.
Industrial controllers are special purpose computers used for controlling industrial processes and manufacturing equipment. Under the direction of a stored program, the industrial controller examines a series of inputs reflecting the status of the control process and changes a series of outputs controlling the industrial process. The inputs and outputs may be binary, that is on or off, or analog providing a value within a continuous range.
An industrial controller differs from a conventional computer in a number of ways. First, unlike a computer, the industrial controller is normally customized to an individual application both by writing new control software stored in the controller's memory, and by changing the hardware configuration of the controller itself.
The ability to reconfigure the controller hardware economically is provided by dividing the industrial controller into a number of modules each performing a different function. Different combinations of the modules may be connected together on a backplane or by one or more communication links. The modules may include, for example, processors, power supplies, communication interfaces and input/output modules. Each module generally incorporates a microprocessor and related circuitry and operates according to a local stored program. Interconnecting the modules over communication links allows the various components of the industrial controller to be separated by a considerable distance over an expanse of a large factory or manufacturing operation. In this way, for example, input and output modules may be located near the portions of the machine from which they receive signals and to which they provide signals.
An industrial controller differs also from a conventional computer in that it is designed to provide "real-time" control, that is control output signals that respond in a near instantaneous manner to changes in the input signals from the controlled process. Generally such real-time control requires the use of a high speed network to communicate data between the I/O modules and the central processor of the industrial controller, and a high speed processor that may scan rapidly through a control program. Particularly for demanding applications such as high speed bottling lines, the delay inherent in this control process may be significant. Accordingly, there is continual effort expended in developing higher speed communication links and increasingly fast processors to minimize any delay.